Reserved for FAQ1
Have to add some things....
For now:
Before starting assembly, take your case and put PCB's inside by the way you like it.
Use 250mm or more case (10' depth).
Don't be greedy on small case, as we already have space-saving brother, MixBuzz500.
Play with pcb's, power trafo, etc, and find a way everything fits fine, mind the place for wires, etc.
Scroll this thread to see pictures to get an idea
http://www.groupdiy.com/index.php?topic=40766
If front panel connected direct to main PCB, first, assemble the case, attach front,
than, connect main, than, mark the holes for main PCB with permanent marker.
Special attention was placed to grounding scheme.
MixBuzz1 have very solid ground scheme, and it is
STAR GROUND, not just a ground plane.
(Reason: to minimize all possible leakages of control signal to audio).
Ground plane is not best here, IMHO.
Central hole on main PCB is the GROUND MECCA. It should be connected to case.
XLR's pin1 connected to case; actually, if input/output wire's lenght
(between pcb and XLR connectors) is less than 5-7 cm, no need for shielded cables, just twist 'em.
Check twice that all components are installed right way.
One wrong resistor can cause PITA for some hours; one wrong placed electrolyt' can
explode and make contamination on PCB (need to wash), but,
HOPEFULLY, you will take a 30 min-hour to CHECK EVERRYTHING and
hopefully everything will be RIGHT
OK than, enough fear and loathing....let's fire up the baby
POWER SUPPLY
will be added soon
After power supply is checked, sonnect it to main PCB.
!!!!!!!!!!!!!!!!!!!
For the next, 1V RMS signal (if not specified) is 1KHZ.
AUDIO
At this stage:
Do not insert any chips into sockets!
Power ON.
Check the voltages with main PCB connected. Let it work 5-10 minutes.
No smoke? Good! Check voltages again.
Power OFF.
Put the VCA's, audio chips (IC1,2,4 L/R).
Pay special attention when inserting the chips into sockets.
VCA's can't go wrong way. See pictures for reference.
Power ON.
Now, check:
Makeup=0, MIX=OFF.
Feed 1V RMS (0DBV) to inputs, press COMP IN (bypass off), check output
is 0DBV (1V RMS). With use of "right" VCA and R6, R3, R100, MF 1%,
the level difference between channels should be less than 0.2db.
BTW, most of people will use soundcards with RMAA to do adjustment;
check your soundcard output 0dbV=1V, some soundcards have 0,2...0.5 db
difference between channels... Some cheap multimters can read less volts on 10kHz AC..
(in other words, me recommend analyzer
Same for noise etc measurements, I use analyzer WITHOUT weighting filters.
Adjust VCA's for minimum distortion. SYML, SYMR pots.
Or, leave some distortion at your taste.
@1Vrms 1kHz input, my MixBuzz1 shows 0.0045% distortion on analyzer, when trimmed best possible way;
SINAD -90db, S/N >94 db, 4x2181B VCA's used.
Readings @5V RMS input: distortion 0.0035%, SINAD-95 db, S/N 106 db.
Frequency responce 15Hz-60kHz: -0.1 db max.
Some words about distortion and noise.
More VCA's=less noise. More VCA's does not means less distortion.
Minimal distortion can be adjusted with use of A grade VCA, IMHO, not worth.
To make good sounding compressor with nice amount of coloration,
use ONE VCA and misadjust SYML/SYMR pots for 0.02-0.06 % of distortion.
More "misadjustment" can cause hearable leakage of control voltage to audio,
it sounds bad imo on fast attack times.
After adjustment and checking, turn power off.
MIX (C&B)
IF MIX NOT USED, INSTALL JUMPERS JP2 L/R
Install C&B (MIX) chips, if you use them, NE5532, OPA275, OPA2604 or OPA2134.
Check the MIX potentiometer connected right way (see MIN-W-MAX markings on PCB).
Shielded wire shoud be used to connect MIX pot,
MOGAMI digital (microphone) audio cable IMHO the best.
Check everything again.
Feed 1V RMS (0dbV) to input.
Power ON; check unity gain again;
MIX on; MIX pot = CENTER, adjust R63& (left channel), R64& (right channel) for same +2Db;
check channels are same in mx. DRY and WET positions (about -2Db), adjust for same levels
if needed.
The level difference between channels should be less than 0.5 DB for all range of MIX pot.
After adjustment and checking, turn power off.
CONTROL and FILTERS
IF SC FILTERS NOT USED, INSTALL JUMPERS JP1 L/R
Put the chips in sockets, check everything twice.
When installing ribbon cables, check twice, because it is easy possible
to make a mistake here.
RATIO=10, THRESHOLD=+15DB, ATTACK=FAST, RELEASE=SLOW, MAKEUP=0, SIDECHAIN=OFF,
MIX=OFF, SC MONO=OFF.
Feed 1V RMS to input, check output is 1VRMS.
Turn THRESHOLD CCW, check the signal changes.
Turn THRESHOLD back to +15.
Turn makeup CW, check output is +19...20db.
Turn makeup back to 0.
Feed 1V RMS to input, check output is 1VRMS.
Check the voltages between TP1 and TP2 to ground, they should be 0.00 V,
adjust SC_SYM L/R trimpots.
Ratios
Feed -10db to input; check output is -10db
Adjust THRESHOLD for -1db output (2db compression).
Adjust make-up to read -10db.
Check RATIO=10; feed +10db input; adjust RATIOS trimpot to get output -8dB (+/-0.1 db)
MAKEUP=0, THRESHOLD=+15DB, RATIO=2
Feed -10db to input; check output is -10db
Adjust THRESHOLD for -12db output (2db compression).
Adjust make-up to read -10db.
Check RATIO=2; feed +10db input; check the output is 0dB (+/-0.5 db)
If analog meter used:
Feed 0dbV to input; check output is 0db
Adjust THRESHOLD for -20 or -10 db output (10 or 20db compression, depending on
maximum scale of your analog meter).
Adjust GR_MTR trimpot for corresponding meter's reading (-10 or -20 db gain reduction).
Now, freq resp of sidechain.
RATIO=10, THRESHOLD=+15DB, ATTACK=FAST, RELEASE=SLOW, MAKEUP=0, SIDECHAIN=OFF,
MIX=OFF, SC MONO=OFF.
Feed 0dbV 1kHz to input; check output is 0db ; adhust THRESHOLD for 10 db compression;
change frequency to 50HZ and 10Khz, check for same amount of compression +/-0.5db.
It is OK if compression @10k is 1db less than @1khz, same way "original" comp behaves too.
RATIO=10, THRESHOLD=+15DB, ATTACK=FAST, RELEASE=SLOW, MAKEUP=0, SIDECHAIN=40,
MIX=OFF, SC MONO=OFF.
Feed 0dbV 1kHz to input; check output is 0db ; adjust THRESHOLD for 10 db compression;
compensate with make-up for 0db;
change frequency to 20HZ, check +8 +/-1db output
SIDECHAIN=80
Feed 0dbV 1kHz to input; check output is 0db ; adjust THRESHOLD for 10 db compression;
compensate with make-up for 0db;
change frequency to 40HZ, check +6 +/-1db output
SIDECHAIN=120
Feed 0dbV 1kHz to input; check output is 0db ; adjust THRESHOLD for 10 db compression;
compensate with make-up for 0db;
change frequency to 80HZ, check +7 +/-1db output
Note. All these 40/80/120 markings are very subjective.
I used the capacitor's values which worked best for ear...the actual filter's freq's
can be bit different.
SIDECHAIN=TL
Feed 0dbV 1kHz to input; check output is 0db ; adjust THRESHOLD for 10 db compression;
compensate with make-up for 0db;
change frequency to 40HZ, check +8 +/-1db output
change frequency to 100HZ, check +4 +/-1db output
change frequency to 5kHZ, check -3 +/-1db output
change frequency to 10kHZ, check -7 +/-1db output
SIDECHAIN=TM
Feed 0dbV 1kHz to input; check output is 0db ; adjust THRESHOLD for 10 db compression;
compensate with make-up for 0db;
change frequency to 40HZ, check +9 +/-1db output
change frequency to 100HZ, check +8 +/-1db output
change frequency to 5kHZ, check -6 +/-1db output
change frequency to 10kHZ, check -7 +/-1db output
The output can be different a bit from these values-10% capacitors, etc,
BUT should be very close for both L/R channels.
METER
Meter calibration
1). Check the OFFSETL, OFFSETR trimpots wipers are connected to GND.
If we look to meter driver board and 10-pin connector is at bottom,
central pins of these trimpots should be connected to bottom pins.
I.e. start adjustment without any offset.
2). Set meter switch to OUT; Feed input about 1V RMS, measure output with
AC RMS voltmeter;
Adjust output with MAKEUP to get 0DB, in case of +4dBU it is 1.22V RMS,
THAN adjust SCALEL, SCALEL to get reading of 0db on LED meter scale.
3). Feed about 0.07V RMS to input, adjust output with MAKEUP to get -22dbU (95mV),
and check meter shows -22dB. If no, adjust little bit OFFSET trimpot for corresponding channel.
Recheck, repeat (2) and (3) if need.
4). Without any input signal, set meter switch to GR; adjust GR_OFFSL trimpot to get
reading of 0dB on LED meter;
5). Feed input signal 1V RMS, NO compression NO makeup, i.e.
threshold is CW, makeup is CCW, check the out is 1V as well;
Adjust THRESHOLD for -20 or -10 db output (10 or 20db compression, depending on
maximum scale of meter you want to use).
Adjust GR_MTR trimpot located at the main PCB for corresponding LED meter's reading
(-10 or -20 db gain reduction)
Recheck, repeat (4) and (5) if need.